Also getting attention will be the magnificent stone frieze depicting Liverpool’s 18th century mercantile wealth by sculpted mermaids crocodiles, elephants and pearls.

Designed originally by John Wood Jnr of Bath the town hall opened in 1754 but was badly damaged by fire in 1795 and was rebuilt by another top Georgian architect, James Wyatt, who added the dome and Castle Street balcony and portico.

Not everyone appreciated its value in times past and an unsuccessful cannon attack was launched from the Mersey during the American War of Independence in 1775.

The Irish Fenians also attempted to blow up the building in 1881.

Steve Gibbs, Liverpool town hall manager, said: “Because the town hall uses sandstone from various quarries it is at least three different colours - pink, beige and brown.

“Restorers even used brown paint in the past to try and match the different work so we’re trying to sort this out too. The town hall will remain open throughout the work.”

Lord Mayor, Councillor Gary Millar, said: “As one of our prized cultural assets we must maintain it to a very high standard and so have brought in heritage experts.”